1. Field of the Invention
The present invention relates to a variable geometry turbocharger having a variable nozzle configured to adjust opening of a flow path for exhaust gas.
2. Description of the Related Art
Turbochargers are disclosed in Japanese Laid-Open Patent Publication No. 2010-270631, Japanese Laid-Open Patent Publication No. 2002-38964, and Japanese Laid-Open Patent Publication 2002-256877. The turbocharger utilizes exhaust gas in order to rotate a turbine and supercharge intake air. This helps to improve the output characteristics of an engine. A variable nozzle is provided in a flow path communicating between an inflow inlet for exhaust gas and an exhaust turbine. The variable nozzle is driven by an actuator according to the RPM of the engine, the amount of exhaust gas, etc., for adjusting an opening of the flow path. As a result, nevertheless there is low rotation in the engine, and the amount of exhaust gas is small, the flow velocity of the exhaust gas can be increased. In this way, it is possible to secure an appropriate turbine RPM, so as to provide an appropriate supercharging pressure.
It should be noted, however, that the turbocharger, in which a driving force is transmitted from the actuator to the variable nozzle, involves a large number of components. Thus, an error is generated in the opening of the variable nozzle due to dimensional errors and mounting errors of the components.
Japanese Laid-Open Patent Publication No. 2010-270631 discloses a variable geometry turbocharger. The variable geometry turbocharger has a torque control means for controlling the output torque of an internal combustion engine. The torque control means has a learning means. The learning means learns the turbocharger individual differences based on the condition of the supercharging pressure. The learning means performs learning such that when the change in the supercharging pressure in a transient stage of the turbocharger is larger than a standard amount, the initial value of the torque control value increases. This helps to suppress the generation of an inadvertent difference in torque level. The learning means performs learning such that when the change in the supercharging pressure in the transient stage is smaller than a standard amount, the initial value of the torque control value decreases. In this way, unnecessary torque control is avoided.
It should be noted, however, that the learning means performs learning after the operation in the transient stage of the turbocharger. Thus, until the learning is completed, there is the possibility of a difference in torque level due to the turbocharger individual differences being generated.
Japanese Laid-Open Patent Publication No. 2002-38964 discloses a method of mounting a turbocharger with a variable nozzle vane. By this method, it is possible to attach a plurality of variable nozzles easily and securely. By this method, it is possible to achieve a reduction in variable nozzle mounting errors. However, since the number of power transmission members transmitting drive force from the actuator to the variable nozzle is large, it is not easy to sufficiently lower the dimensional and mounting errors of these members.
Japanese Laid-Open Patent Publication No. 2002-256877 discloses a nozzle opening regulation apparatus of a variable nozzle mechanism and a method of manufacturing the same. The apparatus or the manufacturing method helps to simplify the opening and closing of the variable nozzle. Thus, it is possible to reduce the assembly man-hours, adjustment operation man-hours, assembly cost, and adjustment operation cost of the variable nozzle mechanism. It is possible to simplify the structure for setting the fully open position and fully closed position, thus achieving a reduction in component cost. However, the number of power transmission members for transmitting the driving force from the actuator to the variable nozzle is rather large. Thus, it is not easy to sufficiently reduce the dimensional and mounting errors of these members.
Thus, there has been a need for a variable geometry turbocharger capable of sufficiently reducing the errors mentioned above.